The technical applicability of hydrochar-derived pyrolysis char-supported Cu nanoparticles composite (Cu NPs/HDPC) to the degradation of octocrylene (OC) was investigated in aqueous solutions in the presence of H2O2. The physico-chemical properties of the Cu NPs/HDPC composite before and after degradation reaction were described. The role of center dot OH in this H2O2-led degradation was examined using electron spin resonance (EPR) technique. The possible degradation mechanisms of OC by the Cu NPs/HDPC-H2O2 system and its degradation pathways were investigated. A relatively large surface area and pore volume of the HDPC (191.4 m(2) g(-1) and 0.11 cm(3) g(-1), respectively) resulted in well-dispersed Cu NPs loading on the surface. The degradation efficiency of OC (50 mu M) was 97.0% in the presence of Cu NPs/HDPC composite (0.5 g L-1) and H2O2 (20 mM) at pH 5.6 in 4 h, which was significantly higher than in Cu NPs/biochar and the integrated HDPC-Cu NPs, i.e., 62.4% and 79.7%, respectively, under the same conditions (ANOVA test; p <= 0.05). Several oxidation by-products of the OC included benzophenone, 3,3-diphenylacrylonitrile, and others. The center dot OH, which resulted from the Fenton-like oxidation between the Cu species and H2O2 on the HDPC surface, was the predominant factor responsible for the OC degradation in the solution. The center dot OH formation was facilitated by a single-electron transfer process from the HDPC surface, in which the Cu NPs/HDPC composite with its C-OH functional group promoted the decomposition of H2O2. These findings contribute to a novel approach of cost-effective wastewater treatment by adding value to unused waste materials from agricultural industries.